1. Field of the Invention
This invention relates to a soy protein with a high molecular weight. The high molecular weight soy protein has desirable flavor and functional properties, such as high water solubility and emulsification and low sedimentation and viscosity.
2. Description of the Related Art
The benefits of soy protein are well documented. Cholesterol is a major concern with consumers throughout the industrialized world. It is well known that vegetable products contain no cholesterol. For decades, nutritional studies have indicated that the inclusion of soy protein in the diet actually reduces serum cholesterol levels in people who are at risk. The higher the cholesterol, the more effective soy proteins are in lowering that level.
Soybeans have the highest protein content of all cereals and legumes. In particular, soybeans have about 40% protein, while other legumes have 20-30%, and cereals have about 8-15% protein. Soybeans also contain about 20% oil with the remaining dry matter mostly carbohydrate (35%). On a wet basis (as is), soybeans contain about 35% protein, 17% oil, 31% carbohydrates, and 4.4% ash.
In the soybean, both storage protein and lipid bodies are contained in the usable meat of the soybean (called the cotyledon). The complex carbohydrate (or dietary fiber) is also contained in the cell walls of the cotyledon. The outer layer of cells (called the seed coat) makes up about 8% of the soybean""s total weight. The raw, dehulled soybean is, depending on the variety, approximately 18% oil, 15% soluble carbohydrates, 15% insoluble carbohydrates, 14% moisture and ash, and 38% protein.
In processing, soybeans are carefully selected for color and size. The soybeans are then cleaned, conditioned (to make removal of the hull easier) and cracked, dehulled and rolled into flakes. The flakes are subjected to a solvent bath that removes the oil. The solvent is removed and the flakes are dried, creating the defatted soy flakes that are the basis of all soy protein products. Despite the large number of products on the market, there are only three types of soy protein: flours, isolates, and concentrates.
Soy flours are the simplest forms of soy protein, having a protein content of approximately 50%. Simply grinding and screening the defatted flakes produces soy flours. This simple processing leaves the soy flour with many of the soybean""s characteristics. Essentially all of the protein of soy flour is in the native form, having a molecular weight of less than about 800,000, as depicted in FIG. 4. The lack of processing also makes soy flours highly variable in terms of quality.
Soy flours and grits are still widely produced and are used most often in baked goods, snack foods and pet foods applications where the high flavor profile does not pose a problem. Textured soy flours were an early attempt at simulating or enhancing the texture of meat products. Texturizing does not change the composition of soy flours and reduces the flavor profile only slightly. Their primary applications are inexpensive meat products or pet foods.
Isolates are produced through standard chemical isolation, drawing the protein out of the defatted flake through solubilization (alkali extraction at pH 7-10) and separation followed by isoelectric precipitation. As a result, isolates are 90% protein on a moisture-free basis. Isolates can be made with a high percentage of soluble protein and a low flavor profile. They contain no dietary fiber and are sometimes high in sodium, properties that can limit their application. Isolate processing is relatively complex and much of the soybean""s protein is lost in the centrifuging process, so the cost of isolates is high. Their major applications have been in dairy substitution, as in infant formulas and milk replacers.
Soy concentrates have at least 60% protein and typically have about 70% protein. A myriad of applications has been developed for soy concentrates and texturized concentrates in processed foods, meat, poultry, fish, cereal and dairy systems.
Soy protein concentrates are made by removing soluble carbohydrate material from defatted soy meal. Aqueous alcohol extraction (60-80% ethanol) or acid leaching (isoelectric pH 4.5) are the most common means for carbohydrate removal. In both aqueous alcohol extraction and acid leaching, however, essentially all of the protein is rendered insoluble. Protein solubility may be recovered in acid leach products by neutralization.
U.S. Pat. No. 4,234,620 (xe2x80x9cHoward et al.xe2x80x9d) describes a method for making water-soluble vegetable protein aggregates from aqueous alcohol extracted soy protein concentrates. The molecular weight profile of the soluble proteins of a product made using the Howard et al. method is depicted in FIG. 3. When viewed in relation to the molecular weight profile of unmodified commercial soy four (FIG. 4) it can be seen that a substantial amount of the soluble proteins in the Howard et al. product are converted to higher molecular weight aggregates.
Howard et al. describes soy products that have at most a nitrogen solubility index (xe2x80x9cNSIxe2x80x9d) of 72. Howard et al. also describes high NSI soy proteins that have at most about 50% by weight of the soluble proteins, or at most about 36% of total proteins, with a molecular weight greater than one million. Further, Howard et al. describes soy protein aggregates that have a substantial portion of their proteins in the 1,000 to 380,000 molecular weight range.
The present invention comprises a vegetable material composition containing highly soluble, high molecular weight vegetable protein aggregates with the structure of the protein not having been modified with an organic solvent, such as aqueous alcohol. More specifically, the present method uses soy flour as a starting material, and aggregates the low molecular weight proteins of the soy flour into high molecular weight proteins without using an organic solvent, such as aqueous alcohol, to modify the structure of the protein.
It is an object of the present invention to make highly soluble, high molecular weight vegetable protein aggregates from soy flour and without using alcohol or other organic solvents to modify the structure of the proteins.
It is further an object of the present invention to produce high NSI soy protein aggregates that have as much as about three-fourths by weight of the soluble proteins, or as much as 64% of the total proteins, with a molecular weight greater than 800,000.
It is further an object of the present invention to produce soy proteins having an NSI greater than 85.
It is further an object of the present invention to make a soy protein product that is essentially absent of proteins in the 1,000 to 380,000 molecular weight range, such that the product contains predominantly high molecular weight protein aggregates and essentially no remainder of unmodified native protein.
It is further an object of the present invention to make soy proteins that have a low degree of sedimentation and a low viscosity.
In another embodiment, the present invention concerns a method for manufacturing a protein product comprising: a) providing a soybean material defatted with hexane; b) adjusting the pH of the material; c) heating the material at an effective temperature for an effective time; d) removing fiber from the material; e) heat treating the material; and f) drying the material. The product may then used in a liquid or dry beverage, food or nutritional product.
In one form thereof, the present invention provides a vegetable material composition comprising highly soluble, high molecular weight vegetable protein aggregates, wherein the structure of the proteins has not been modified with an organic solvent.
In another form thereof, the present invention provides a soy protein product made from a soy material having less than about 5% by weight of the protein in the material of a molecular weight greater than about 800,000, wherein a solvent is not used to modify the structure of the protein in the material, and wherein the product has at least about 55% by weight of protein of total dry matter of the product, a nitrogen solubility index (NSI) of at least about 85, and at least about 65% by weight of the protein in the product has a molecular weight greater than about 800,000.
In another form thereof, the present invention provides a method of making a soy protein product from a soy material, including the steps of slurrying the soy material in water, with the material being substantially defatted; adjusting the pH of the material; removing fiber from the material; and heating the material.
In another form thereof, the present invention provides a liquid or dry beverage, food or nutritional product, including a soy protein product made by a process including the steps of slurrying the soy material in water, with the material being substantially defatted; adjusting the pH of the material; removing fiber from the material; and heating the material.
In another form thereof, the present invention provides a vegetable material composition including highly soluble, high molecular weight vegetable protein aggregates, the composition having a nitrogen solubility index (NSI) greater than about 85.
In another form thereof, the present invention provides a vegetable material composition including highly soluble, high molecular weight vegetable protein aggregates, wherein about 75% by weight of the protein aggregates have a molecular weight greater than 380,000.
In still another form thereof, the present invention provides a vegetable material composition including highly soluble, high molecular weight vegetable protein aggregates, wherein at least about 65% by weight of the protein aggregates have a molecular weight greater than about 800,000.